Network Working Group D. Farinacci Internet-Draft V. Fuller Intended status: Experimental D. Meyer Expires: August 9, 2009 Cisco February 5, 2009 LISP Alternative Topology (LISP+ALT) draft-fuller-lisp-alt-04.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 9, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Farinacci, et al. Expires August 9, 2009 [Page 1] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 Abstract This document describes a method of building an alternative, logical topology for managing Endpoint Identifier to Routing Locator mappings using the Locator/ID Separation Protocol. The logical network is built as an overlay on the public Internet using existing technologies and tools, specifically the Border Gateway Protocol and the Generic Routing Encapsulation. An important design goal for LISP+ALT is to allow for the relatively easy deployment of an efficient mapping system while minimizing changes to existing hardware and software. Table of Contents 1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 5 4. The LISP 1.5 model . . . . . . . . . . . . . . . . . . . . . . 7 5. LISP+ALT: Overview . . . . . . . . . . . . . . . . . . . . . . 8 5.1. ITR traffic handling . . . . . . . . . . . . . . . . . . . 8 5.2. EID Assignment - Hierarchy and Topology . . . . . . . . . 9 5.3. LISP+ALT Router . . . . . . . . . . . . . . . . . . . . . 10 5.4. ITR and ETR in a LISP+ALT Environment . . . . . . . . . . 10 5.5. Use of GRE and BGP between LISP+ALT Routers . . . . . . . 11 6. EID-to-RLOC mapping propagation . . . . . . . . . . . . . . . 12 6.1. Changes to ITR behavior with LISP+ALT . . . . . . . . . . 12 6.2. Changes to ETR behavior with LISP+ALT . . . . . . . . . . 12 7. BGP configuration and protocol considerations . . . . . . . . 14 7.1. Autonomous System Numbers (ASNs) in LISP+ALT . . . . . . . 14 7.2. Sub-Address Family Identifier (SAFI) for LISP+ALT . . . . 14 8. EID-Prefix Aggregation . . . . . . . . . . . . . . . . . . . . 15 8.1. Traffic engineering with LISP and LISP+ALT . . . . . . . . 15 8.2. Edge aggregation and dampening . . . . . . . . . . . . . . 16 9. Connecting sites to the ALT network . . . . . . . . . . . . . 17 9.1. ETRs originating information into the ALT . . . . . . . . 17 9.2. ITRs Receiving Information from the ALT . . . . . . . . . 17 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 11. Security Considerations . . . . . . . . . . . . . . . . . . . 20 11.1. Apparent LISP+ALT Vulnerabilities . . . . . . . . . . . . 20 11.2. Survey of LISP+ALT Security Mechanisms . . . . . . . . . . 21 11.3. Using existing BGP Security mechanisms . . . . . . . . . . 21 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 13.1. Normative References . . . . . . . . . . . . . . . . . . . 23 13.2. Informative References . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 Farinacci, et al. Expires August 9, 2009 [Page 2] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 1. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Farinacci, et al. Expires August 9, 2009 [Page 3] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 2. Introduction This document describes a method of building an alternative logical topology for managing Endpoint identifier to Routing Locator mappings using the Locator/ID Separation Protocol [LISP]. This logical topology uses existing technology and tools, specifically the Border Gateway Protocol [RFC4271] and its multi-protocol extension [RFC2858], along with the Generic Routing Encapsulation [RFC2784] protocol to construct an overlay network of devices that advertise EID-prefixes only. These Endpoint Identifier Prefix Aggregators hold hierarchically-assigned pieces of the Endpoint Identifier space (i.e., prefixes) and their next hops toward the network element which is authoritative for Endpoint Identifier-to-Routing Locator mapping for that prefix. Tunnel routers can use this overlay to make queries against and respond to mapping requests made against the distributed Endpoint Identifier-to-Routing Locator mapping database. Note the database is distributed (as described in [LISP]) and is stored in the ETRs. Note that an important design goal of LISP+ALT is to minimize the number of changes to existing hardware and/or software that are required to deploy the mapping system. It is envisioned that in most cases existing technology can be used to implement and deploy LISP+ ALT. Since the deployment of LISP+ALT adds new devices to the network, existing devices not need changes or upgrades. They can function as they are to realize an underlying and robust physical topology. The remainder of this document is organized as follows: Section 3 provides the definitions of terms used in this document. Section 4 outlines the basic LISP 1.5 model. Section 5 provides a basic overview of the LISP Alternate Topology architecture, and Section 6 describes how the ALT uses BGP to propagate Endpoint Identifier reachability over the overlay network. Section 8 describes the construction of the ALT aggregation hierarchy, and Section 9 discusses how LISP+ALT elements are connected to form the overlay network. Farinacci, et al. Expires August 9, 2009 [Page 4] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 3. Definition of Terms LISP+ALT operates on two name spaces and introduces a new network element, the LISP+ALT Router (see below). This section provides high-level definitions of the LISP+ALT name spaces, network elements, and message types. The Alternative Logical Topology (ALT): The virtual overlay network made up of tunnels between EID Prefix Aggregators. The Border Gateway Protocol (BGP) runs between LISP+ALT routers and is used to carry reachability information for EID prefixes. Legacy Internet: The portion of the Internet which does not run LISP and does not participate in LISP+ALT. LISP+ALT Router: The devices which run on the ALT. The ALT is a static network built using tunnels between LISP+ALT routers. These routers are deployed in a hierarchy in which routers at each level in the this hierarchy are responsible for aggregating all EID prefixes learned from those logically "below" them and advertising summary prefixes to the routers logically "above" them. All prefix learning and propagation between levels is done using BGP. LISP+ALT routers at the lowest level, or "edge", of the ALT learn EID prefixes either over a BGP session to ETRs or through static routes (in the case of the "low-opex ETR"). See Section 7 for details on how BGP is configured between the different network elements. The primary function of LISP+ALT routers is to provide a lightweight forwarding infrastructure for LISP control-plane messages (Map-Request and Map-Reply), and to transport data packets when the packet has the same destination address in both the inner (encapsulating) destination and outer destination addresses ((i.e., a Data Probe packet). Endpoint ID (EID): A 32-bit (for IPv4) or 128-bit (for ipv6) value used in the source and destination address fields of the first (most inner) LISP header of a packet. A packet that is emitted by a system contains EIDs in its headers and LISP headers are prepended only when the packet reaches an Ingress Tunnel Router (ITR) on the data path to the destination EID. In LISP+ALT, EID-prefixes MUST BE assigned in a hierarchical manner (in power-of-two) such that they can be aggregated by LISP+ ALT routers. In addition, a site may have site-local structure in how EIDs are topologically organized (subnetting) for routing within the site; this structure is not visible to the global routing system. Farinacci, et al. Expires August 9, 2009 [Page 5] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 EID-Prefix Aggregate: A set of EID-prefixes said to be aggregatable in the [RFC4632] sense. That is, an EID-Prefix aggregate is defined to be a single contiguous power-of-two EID-prefix block. Such a block is characterized by a prefix and a length. Routing Locator (RLOC): An IP address of an egress tunnel router (ETR). It is the output of a EID-to-RLOC mapping lookup. An EID maps to one or more RLOCs. Typically, RLOCs are numbered from topologically-aggregatable blocks that are assigned to a site at each point to which it attaches to the global Internet; where the topology is defined by the connectivity of provider networks, RLOCs can be thought of as Provider Aggregatable (PA) addresses. Note that in LISP+ALT, RLOCs are not carried by LISP+ALT routers. EID-to-RLOC Mapping: A binding between an EID and the RLOC-set that can be used to reach the EID. The term "mapping" refers to an EID-to-RLOC mapping. EID Prefix Reachability: An EID prefix is said to be "reachable" if one or more of its locators are reachable. That is, an EID prefix is reachable if the ETR (or its proxy) that is authoritative for a given EID-to-RLOC mapping is reachable. Default Mapping: A Default Mapping is a mapping entry for EID- prefix 0.0.0.0/0. It maps to a locator-set used for all EIDs in the Internet. If there is a more specific EID-prefix in the mapping cache it overrides the Default Mapping entry. The Default Mapping route can be learned by configuration or from a Map-Reply message. Default Route: A Default Route in the context of LISP+ALT is a EID- prefix value of 0.0.0.0/0 which is advertised by BGP on top of the ALT. The Default Route is used to realize a path for Data Probe or Map-Request packets. Farinacci, et al. Expires August 9, 2009 [Page 6] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 4. The LISP 1.5 model As documented in [LISP], the LISP 1.5 model uses the same basic query/response protocol machinery as LISP 1.0. In particular, LISP+ ALT provides two mechanisms for an ITR to obtain EID-to-RLOC mappings (both of these techniques are described in more detail in Section 9.2): Data Probe: An ITR may send the first few data packets into the ALT to minimize packet loss and to probe for the mapping; the authoritative ETR will respond to the ITR with a Map-Reply message when it receives the data packet over the ALT. Note that in this case, the inner Destination Address (DA), which is an EID, is copied to the outer DA and is routed over the ALT. Map-Request: An ITR may also send a Map-Request message into the ALT to request the mapping. As in the Data Probe case, the authoritative ETR will respond to the ITR with a Map-Reply message. In this case, the DA of the Map-Request MUST be an EID. See [LISP] for the format of Map-Request and Map-Reply packets. Like LISP 1.0, EIDs are routable and can be used, unaltered, as the source and destination addresses in IP datagrams. Unlike in LISP 1.0, LISP 1.5 EIDs are not routable on the public Internet; instead, they are only routed over a separate, virtual topology referred to as the LISP Alternative Virtual Network. This network is built as an overlay on the public Internet using tunnels to interconnect LISP+ALT routers. BGP is run over these tunnels to propagate the information needed to route Data Probes and Map-Request/Replies. Importantly, while the ETRs are the source(s) of the unaggregated EID prefix data, LISP+ALT uses existing BGP mechanisms to aggressively aggregate this information. Note that ETRs are not required to participate (or prevented from participating) in LISP+ALT; they may choose communicate their mappings to their serving LISP+ALT router(s) at subscription time via configuration. ITRs are also not required to participate in (nor prevented from participating in) LISP+ALT. Farinacci, et al. Expires August 9, 2009 [Page 7] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 5. LISP+ALT: Overview LISP+ALT is a hybrid push/pull architecture. Aggregated EID prefixes are "pushed" among the LISP+ALT routers and, optionally, out to ITRs (which may elect to receive the aggregated information, as opposed to simply using a default mapping). Specific EID-to-RLOC mappings are "pulled" by ITRs when they either send explicit LISP requests or data packets on the alternate topology that result in triggered replies being generated by ETRs. The basic idea embodied in LISP+ALT is to use BGP, running over an overlay network made up of Generic Routing Encapsulation (GRE) tunnels, to establish reachability required to route Data Probes, Map-Requests, and Map-Replies over the alternate topology (ALT). The ALT RIB (BGP RIB) is comprised of EID prefixes (and associated next hops). The LISP+ALT routers talk eBGP to each other in order to propagate EID prefix update information, which is learned either over eBGP connections from the authoritative ETR, or by configuration. ITRs may also eBGP peer with one or more LISP+ALT routers in order to route Data Probe packets or Map-Requests (more likely, an ITR will have a default mapping pointing at one or more LISP+ALT routers). Note that while this document explicitly specifies the use of GRE as a tunneling mechanism, there is no reason that a ALT cannot be built using other tunneling technologies. In cases where GRE does not meet security, management, or other operational requirements, it is reasonable to use another tunneling technology that does. References to "GRE tunnel" in later sections of this document should therefore not be taken as prohibiting or precluding the use of other, available tunneling mechanisms. In summary, LISP+ALT uses BGP to propagate EID-prefix update information used by ITRs and ETRs to forward Map-Requests, Map- Replies, and Data Probes. This reachability is carried as IPv4 or IPv6 NLRI without modification (since the EID space has the same syntax as IPv4 or IPv6). LISP+ALT routers eBGP peer with one another, forming the ALT. An LISP+ALT router near the edge learns EID prefixes which are originated by authoritative ETRs, either by eBGP peering with them or by configuration. LISP+ALT routers aggregate EID prefixes, and forward Data Probes, Map-Requests, and Map-Replies. 5.1. ITR traffic handling When an ITR receives a packet originated by an end system within its site (i.e. a host for which the ITR is the exit path out of the site) and the destination for that packet is not known in the ITR's mapping cache, the ITR encapsulates the packet in a LISP header, copying the Farinacci, et al. Expires August 9, 2009 [Page 8] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 inner destination address (EID) to the outer destination address (RLOC), and transmits it through a GRE tunnel to a LISP+ALT router in the ALT. This "first hop" LISP+ALT router uses EID-prefix routing information learned from other LISP+ALT routers via BGP to guide the packet to the ETR which "owns" the prefix. Upon receipt by the ETR, normal LISP processing occurs: the ETR responds to the ITR with a LISP Map-Reply that lists the RLOCs (and, thus, the ETRs to use) for the EID prefix. The ETR also de-encapsulates the packet and transmits it toward its destination. Upon receipt of the Map-Reply, the ITR installs the RLOC information for a given prefix into a local mapping database. With these mapping entries stored, additional packets destined to the given EID prefix are routed directly to a viable ETR without use of the ALT, until either the entry's TTL has expired, or the ITR can otherwise find no reachable ETR. Note that a valid mapping (not timed-out) may exist that contains no reachable RLOCs (i.e. all paths to that ETR are down); in this case, packets destined to the EID prefix are dropped, not routed through the ALT. Traffic routed over the ALT therefore consists of: o EID prefix Map-Requests, and o data packets destined for those EID prefixes while the ITR awaits map replies 5.2. EID Assignment - Hierarchy and Topology EID-prefixes will be allocated to a LISP site by Internet Registries. Multiple allocations may not be in power-of-2 blocks. But when they are, they will be aggregated into a single, advertised EID-prefix. The ALT network is built in a tree-structured hierarchy to allow aggregation at merge points in the tree. Building such a structure should minimize the number of EID-prefixes carried by LISP+ALT nodes near the top of the hierarchy. Since the ALT will not need to change due to subscription or policy reasons, the topology can remain relatively static and aggregation can be sustained. Because routing on the ALT uses BGP, the same rules apply for generating aggregates; in particular, a LISP+ALT router should only be configured to generate an aggregate if it is configured with BGP sessions to all of the originators of components (more-specifics prefixes) of that aggregae; not all of the components of need to be present for the aggregate to be originated (some may be holes in the covering prefix and some may be down) but the aggregating router must be configured to learn the state of all of the components. Farinacci, et al. Expires August 9, 2009 [Page 9] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 As an example, consider ETRs that are originating EID prefixes for 10.1.0.0/24, 10.1.64.0/24, 10.1.128.0/24, and 10.1.192.0/24. An ALT router should only be configured to generate an aggregate for 10.1.0.0/16 if it has BGP sessions configured with all of these ETRs, in other words, only if it has sufficient knowledge about the state of those prefixes to summarize them. Under what circumstances the ALT router actually generates the aggregate is a matter of local policy: in some cases, it will be statically configured to do so at all times with a "static discard" route. In other cases, it may be configured to only generate the aggregate prefix if at least one of the components of the aggregate is learned via BGP. This implies that two ALTs that share an overlapping set of prefixes must exchange those prefixes if either is to generate and export a covering aggregate for those prefixes. It also implies that an ETR that originates a prefix must maintain BGP sessions with all ALT routers that are configured to originate an aggregate which covers that prefix. Note: much is currently uncertain about the best way to build the ALT network; as testing and prototype deployment proceeds, a guide to how to best build the ALT network will be developed. 5.3. LISP+ALT Router A LISP+ALT Router has the following functionality: 1. It runs, at a minimum, the eBGP part of the BGP protocol. 2. It supports a separate RIB which uses next-hop GRE tunnel interfaces for forwarding Data Probes and Map-Requests. 3. It can act as a "proxy-ITR" to support non-LISP sites. 4. It can act as an ETR, or as a recursive or re-encapsulating ITR to reduce mapping tables in site-based LISP routers. 5.4. ITR and ETR in a LISP+ALT Environment An ITR using LISP+ALT may have additional functionality as follows: 1. If it is also acting as a LISP+ALT Router, it sends Data Probes or Map-Requests on the BGP best path computed GRE tunnel for each EID prefix. Farinacci, et al. Expires August 9, 2009 [Page 10] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 2. When acting solely as a ITR, it sends Data Probes or Map-Requests directly to a configured LISP+ALT router. An ETR using LISP+ALT may also behave slightly differently: 1. If it is also acting as a LISP+ALT router, it advertises its configured EID-prefixes into BGP for distribution through the ALT. 2. It receives Data Probes and Map-Requests only over GRE tunnel(s) to its "upstream" LISP+ALT router(s) and responds with Map- Replies for the EID prefixes that it "owns". 5.5. Use of GRE and BGP between LISP+ALT Routers The ALT network is built using GRE tunnels between LISP+ALT routers. eBGP sessions are configured over those tunnels, with each LISP+ALT router acting as a separate AS "hop" in a Path Vector for BGP. For the purposes of LISP+ALT, the AS-path is used solely as a shortest- path determination and loop-avoidance mechanism. Because all next- hops are on tunnel interfaces, no IGP is required to resolve those next-hops to exit interfaces. LISP+ALT's use of GRE and BGP reduces provider Operational Expense (OPEX) because no new protocols need to be either defined or used on the overlay topology. Also, since tunnel IP addresses are local in scope, no coordination is needed for their assignment; any addressing scheme (including private addressing) can be used for tunnel addressing. Farinacci, et al. Expires August 9, 2009 [Page 11] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 6. EID-to-RLOC mapping propagation As described in Section 9.2, an ITR may send either a Map-Request or a data probe to find a given EID-to-RLOC mapping. The ALT provides the infrastructure that allows these requests to reach the authoritative ETR. Note that Map-Replies are not sent over the ALT - an ETR always sends a Map-Reply to the source RLOC learned from the original Map-Request. LISP+ALT routers propagate mapping information for use by ITRs (when making Map-Requests or sending Data Probes), and ETRs (if the ETR is configured to send Map-Replies back to the requesting ITR over the ALT) using eBGP [RFC4271]. eBGP is run on the inter-LISP+ALT router links, and and possibly between an edge LISP+ALT router and an ETR or between an edge LISP+ALT router and an ITR. The ALT eBGP RIB consists of aggregated EID prefixes and their next hops toward the authoritative ETR for that EID prefix. 6.1. Changes to ITR behavior with LISP+ALT When using LISP+ALT, an ITR always sends either Data Probes or Map- Requests to one of its "upstream" LISP+ALT routers. As in basic LISP, it should use one of its RLOCs as the source address of these queries; it should explicitly not use a tunnel interface as the source address as doing so will cause replies to be forwarded over the tunneled topology and may be problematic if the tunnel interface address is not explicitly routed throughout the ALT. If the ITR is running BGP with the LISP+ALT router(s), it selects the appropriate LISP+ALT router based on the BGP information received. If it is not running BGP, it uses static configuration to select a LISP+ALT router; in the general case, this will effectively be an "EID-prefix default route". 6.2. Changes to ETR behavior with LISP+ALT If an ETR connects using BGP to one or more LISP+ALT router(s), it simply announces its EID-prefix to those LISP+ALT routers. In the "low-opex" case, where the ETR does not use BGP, it will still have a GRE tunnel to one or more LISP+ALT routers; these LISP+ALT router(s) the ETR must route Map-Requests and Data Probes to the ETR and contain configuration (in effect, static routes) for the ETR's EID- prefixes. Note that in either case, when an ETR generates a Map- Reply message to return to a querying ITR, it sends it to the ITR's source-RLOC (i.e., on the underlying Internet topology, not on the ALT; this avoids any latency penalty that might be incurred by routing over the ALT). Farinacci, et al. Expires August 9, 2009 [Page 12] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 See also Section 9 for more details about the "low-opex" ETR and ITR configurations. Farinacci, et al. Expires August 9, 2009 [Page 13] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 7. BGP configuration and protocol considerations 7.1. Autonomous System Numbers (ASNs) in LISP+ALT The primary use of BGP today is to define the global Internet routing topology in terms of its participants, known as Autonomous Systems. LISP+ALT specifies the use of BGP to create a global EID-to-RLOC mapping database which, while related to the global routing database, serves a very different purpose and is organized into a very different hierarchy. Because LISP+ALT does use BGP, however, it uses ASNs in the paths that are propagated among LISP+ALT routers. To avoid confusion, it needs to be stressed that that these LISP+ALT ASNs use a new numbering space that is unrelated to the ASNs used by the global routing system. Exactly how this new space will be assigned and managed will be determined during experimental deployment of LISP+ALT. Note that the LISP+ALT routers that make up the "core" of the ALT will not be associated with any existing core-Internet ASN because topology, hierarchy, and aggregation boundaries are completely separate from and independent of the global Internet routing system. 7.2. Sub-Address Family Identifier (SAFI) for LISP+ALT As defined by this document, LISP+ALT may be implemented using BGP without modification. Given the fundamental operational difference between propagating global Internet routing information (the current, dominant use of BGP) and managing the global EID-to-RLOC database (the use of BGP proposed by this document), it may be desirable to assign a new SAFI [RFC2858] to prevent operational confusion and difficulties, including the inadvertent leaking of information from one domain to the other. At present, this document does not require the assignment of a new SAFI but the authors anticipate that experimentation may suggest the need for one in the future. Farinacci, et al. Expires August 9, 2009 [Page 14] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 8. EID-Prefix Aggregation The ALT BGP peering topology should be arranged in a tree-like fashion (with some meshiness), with redundancy to deal with node and link failures. A basic assumption is that as long as the routers are up and running, the underlying topology will provide alternative routes to maintain BGP connectivity among LISP+ALT routers. Note that, as mentioned in Section 5.2, the use of BGP by LISP+ALT requires that information can only be aggregated where all active more-specific prefixes of a generated aggregate prefix are known. This implies, for example, that if a given set of prefixes is used by multiple, ALT networks, those networks must interconnect and share information about all of the prefixes if either were to generate an aggregate prefix that covered all of them. This is no different than the way that BGP route aggregation works in the existing global routing system: a service provider only generates an aggregate route if it is configured to learn to all prefixes that make up that aggregate. 8.1. Traffic engineering with LISP and LISP+ALT It is worth noting that LISP+ALT does not directly propagate EID-to- RLOC mappings. What it does is provide a mechanism for a LISP ITR to find the ETR that holds the mapping for a particular EID prefix. This distinction is important for several reasons. First, it means that the reachability of RLOCs is learned through the LISP ITR-ETR exchange so "flapping" of state information through BGP is not likely nor can mapping information become "stale" by slow propagation through the ALT BGP mesh. Second, by deferring EID-to-RLOC mapping to an ITR-ETR exchange, it is possible to perform site-to-site traffic engineering through a combination of setting the preference and weight fields and by returning more-specific EID-to-RLOC information in LISP Map-Reply messages. This is a powerful mechanism that can conceivably replace the traditional practice of routing prefix deaggregation for traffic engineering purposes. Rather than propagating more-specific information into the global routing system for local- or regional-optimization of traffic flows, such more- specific information can be exchanged, through LISP (not LISP+ALT), on an as-needed basis between only those ITRs/ETRs (and, thus, site pairs) that need it; should a receiving ITR decide that it does not wish to store such more-specific information, it has the option of discarding it as long as a shorter, covering EID prefix exists. Not only does this greatly improve the scalability of the global routing system but it also allows improved traffic engineering techniques by allowing richer and more fine-grained policies to be applied. Farinacci, et al. Expires August 9, 2009 [Page 15] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 8.2. Edge aggregation and dampening Note also that normal BGP best common practices apply to the ALT network. In particular, first-hop ALT routers will aggregate EID prefixes and dampen changes to them in the face of excessive updates. Since EID-to-RLOC mappings are not expected to change with anywhere near the frequency as BGP prefix reachability on the Internet, such dampening should be very rare and might be worthy of logging as an exceptional event. Farinacci, et al. Expires August 9, 2009 [Page 16] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 9. Connecting sites to the ALT network 9.1. ETRs originating information into the ALT EID prefix information is originated into the ALT by two different mechanisms: eBGP: An ETR may participate in the LISP+ALT overlay network by running eBGP to one or more LISP+ALT router(s) over GRE tunnel(s). In this case, the ETR advertises reachability for its EID prefixes over these eBGP connection(s). The LISP+ALT router(s) that receive(s) these prefixes then propagate(s) them into the ALT. Here the ETR is simply an eBGP peer of LISP+ALT router(s) at the edge of the ALT. Where possible, a LISP+ALT router that receives EID prefixes from an ETR via eBGP should aggregate that information. Configuration: One or more LISP+ALT router(s) may be configured to originate an EID prefix on behalf of the non-BGP-speaking ETR that is authoritative for a prefix. As in the case above, the ETR is connected to LISP+ALT router(s) using GRE tunnel(s) but rather than BGP being used, the LISP+ALT router(s) are configured with what are in effect "static routes" for the EID prefixes "owned" by the ETR. The GRE tunnel is used to route Map-Requests to the ETR (if necessary), and for the ETR to respond with Map-Replies. Of course, the LISP+ALT router could also serve as a proxy for its TCP-connected ETRs. Note: in both cases, an ETR may have connections to to multiple LISP+ALT routers for the following reasons: * redundancy, so that a particular ETR is still reachable through the ALT even if one path or tunnel is unavailable. * to connect to different parts of the ALT hierarchy if the ETR "owns" multiple EID-to-RLOC mappings for EID prefixes that cannot be aggregated by the same LISP+ALT router (i.e. are not topologically "close" to each other in the ALT). 9.2. ITRs Receiving Information from the ALT In order to source Map-Requests to the ALT and receive Map-Replies from the ALT, or to route a Data Probe packet over the ALT, each ITR participating in the ALT establishes a connection to one or more LISP+ALT routers. These connections can be either eBGP or TCP (as described above). In the case in which the ITR is running eBGP, the peer LISP+ALT Farinacci, et al. Expires August 9, 2009 [Page 17] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 routers use these connections to advertise highly aggregated EID- prefixes to the peer ITRs. The ITR then installs the received prefixes into a forwarding table that is used to to send LISP Map- Requests to the appropriate LISP+ALT router. In most cases, a LISP+ ALT router will send a default mapping to its client ITRs so that they can send request for any EID prefix into the ALT. In the case in which the ITR is connected to some set of LISP+ALT routers without eBGP, the ITR sends Map-Requests to any of its connected LISP+ALT routers, and receives Map-Replies from the LISP+ ALT router that has the "shortest path" to the authoritative ETR. An ITR may also choose to send the first few data packets over the ALT to minimize packet loss and reduce mapping latency. In this case, the data packet serves as a mapping probe (Data Probe) and the ETR which receives the data packet (over the ALT) responds with a Map-Reply that is either routed back over the ALT or send to the ITR's source-RLOC over the underlying topology. In general, an ITR will establish connections only to LISP+ALT routers at the "edge" of the ALT (typically two for redundancy) but there may also be situations where an ITR would connect to other LISP+ALT routers to receive additional, shorter path information about a portion of the ALT of interest to it. This can be accomplished by establishing GRE tunnels between the ITR and the set of LISP+ALT routers with the additional information. This is a purely local policy issue between the ITR and the LISP+ALT routers in question. Farinacci, et al. Expires August 9, 2009 [Page 18] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 10. IANA Considerations This document makes no request of the IANA. Farinacci, et al. Expires August 9, 2009 [Page 19] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 11. Security Considerations LISP+ALT shares many of the security characteristics of BGP. Its security mechanisms are comprised of existing technologies in wide operational use today. Securing LISP+ALT is much simpler than securing BGP. Compared to BGP, LISP+ALT routers are not topologically bound, allowing them to be put in locations away from the vulnerable AS border (unlike eBGP speakers). 11.1. Apparent LISP+ALT Vulnerabilities This section briefly lists of the apparent vulnerabilities of LISP+ ALT. Mapping Integrity: Can an attacker insert bogus mappings to black- hole (create a DoS) or intercept LISP data-plane packets? LISP+ALT router Availability: Can an attacker DoS the LISP+ALT routers connected to a given ETR? without access to its mappings, a site is essentially unavailable. ITR Mapping/Resources: Can an attacker force an ITR or LISP+ALT router to drop legitimate mapping requests by flooding it with random destinations that it will have to query for. Further study is required to see the impact of admission control on the overlay network. EID Map-Request Exploits for Reconnaissance: Can an attacker learn about a LISP destination sites' TE policy by sending legitimate mapping requests messages and then observing the RLOC mapping replies? Is this information useful in attacking or subverting peer relationships? Note that LISP 1.0 has a similar data-plane reconnaissance issue. Scaling of LISP+ALT router Resources: Paths through the ALT may be of lesser bandwidth than more "direct" paths; this may make them more prone to high-volume denial-of-service attacks. UDP Map-Reply from ETR: If Map-Replies packets are sent directly from the ETR to the ITR's RLOC, the ITR's RLOC may be vulnerable to various types of DoS attacks. Farinacci, et al. Expires August 9, 2009 [Page 20] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 11.2. Survey of LISP+ALT Security Mechanisms Explicit peering: The devices themselves can both prioritize incoming packets as well as potentially do key checks in hardware to protect the control plane. Use of TCP to connect elements: This makes it difficult for third parties to inject packets. Use of HMAC Protected TCP Connections: HMAC is used to verify message integrity and authenticity, making it nearly impossible for third party devices to either insert or modify messages. Message Sequence Numbers and Nonce Values in Messages: This allows for devices to verify that the mapping-reply packet was in response to the mapping-request that they sent. 11.3. Using existing BGP Security mechanisms LISP+ALT's use of BGP allows for the ALT to take advantage of BGP security features designed for existing Internet BGP use. For example, should either sBGP [I-D.murphy-bgp-secr] or soBGP [I-D.white-sobgparchitecture] become widely deployed it expected that LISP+ALT could use these mechanisms to provide authentication of EID- to-RLOC mappings, and EID origination. Farinacci, et al. Expires August 9, 2009 [Page 21] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 12. Acknowledgments Many of the ideas described in this document were developed during detailed discussions with Scott Brim and Darrel Lewis, who made many insightful comments on earlier versions of this document. Farinacci, et al. Expires August 9, 2009 [Page 22] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 13. References 13.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz, "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, August 2006. 13.2. Informative References [I-D.murphy-bgp-secr] Murphy, S., "BGP Security Analysis", draft-murphy-bgp-secr-04 (work in progress), November 2001. [I-D.white-sobgparchitecture] White, R., "Architecture and Deployment Considerations for Secure Origin BGP (soBGP)", draft-white-sobgparchitecture-00 (work in progress), May 2004. [LISP] Farinacci, D., Oran, D., Fuller, V., and D. Meyer, "Locator/ID Separation Protocol (LISP)", draft-farinacci-lisp-10.txt (work in progress), November 2008. Farinacci, et al. Expires August 9, 2009 [Page 23] Internet-Draft LISP Alternative Topology (LISP+ALT) February 2009 Authors' Addresses Dino Farinacci Cisco Tasman Drive San Jose, CA 95134 USA Email: dino@cisco.com Vince Fuller Cisco Tasman Drive San Jose, CA 95134 USA Email: vaf@cisco.com Dave Meyer Cisco Tasman Drive San Jose, CA 95134 USA Email: dmm@cisco.com Farinacci, et al. Expires August 9, 2009 [Page 24]